This invention relates to fault monitoring circuits and in particular to a fault monitoring circuit for picking up a relay in response to the monitored signal exceeding a first predetermined level and dropping out the relay in response to the monitored signal falling below a second predetermined level lower than the first predetermined level.
In one type of monitor and relay driver circuit it is desirable to have the monitor circuit responsive to a first predetermined signal level for picking up the relay, and to have the monitor circuit responsive to a second lower predetermined signal level for dropping out the relay once the relay has been picked up.
A problem arises when a voltage or a current responsive monitor and relay driver circuit is used to determine when the amplitude of a series of recurring pulses exceeds a first predetermined magnitude. If the amplitude of the input pulses falls below the drop out level of the relay, and there is sufficient time between pulses for the relay to actually drop out, the relay contacts will chatter. It is desirable to eliminate this relay chatter.
It is, therefore, one object of this invention to provide a monitor and relay driver circuit that responds to a first predetermined signal level for picking up the relay but responds to a second, lower, predetermined signal level for dropping out the relay after the relay has been picked up.
It is another object of this invention to provide a monitor and relay driver circuit that will not allow the contacts of the relay to chatter when used to monitor the amplitude of a series of recurring pulses.